This invention relates generally to a cap for pipes and, more particularly, to a blow off cap for use in conjunction with a vent stack cover, a vent stack containing a pressure relief valve, or a vent stack which utilizes a rupture disk
This invention is directed to providing a suitable blow off cap designed to be utilized in combination with a vent stack or vent pipe used with tanks found in the petroleum, water/food service, and chemical industries. Such tanks often make use of vent stacks to provide for the rapid release of vapor or liquid in the event of sudden extreme pressurization within the tank. There are two potential dangers associated with vent stacks. The first danger relates to the presence of an open vent stack by which airborne contaminants such as water, dust, and pollutants may proceed down the vent stack to the tank itself, thereby contaminating the contents. Thus, the potential exists that the contents of the tank may have to be destroyed due to contamination. The second problem is far more dangerous however, since the resultant situation could include the explosion of the tank itself.
Some vent stacks include a pressure relief valve or rupture disk. When closed the valve o disk prevents contamination of the contents of the tank. In the event of extreme overpressurization, in theory the valve opens or the disk ruptures, thus permitting liquid or vapor to escape. However, excess moisture, dirt, or animal nests, especially those of birds, and more particularly mud daubers, may prevent the pressure relief valve or rupture disk from adequately being able to do their jobs. Thus, users of these tanks found it desirable to try to remedy the situation.
Prior attempts at providing a cover for these vent stacks or pipes included inserting rolled up newspaper into the opening at the top of the pipe, covering the top of a pipe with a cap hand formed from aluminum foil, draping the top of the pipe with a clear plastic sandwich bag, or installing a elaborate manifold system. Still other companies not willing to spend the money or dissatisfied by the almost primitive nature of the precautionary techniques available, chose to take their chances with the elements. Of all of the above methods, most companies today choose to use a clear plastic bag.
However, this method has two grave shortcomings. First, the bags often sag under the weight of precipitation or animal nests. The subsequently sagged bag is then subject to deteriorating through the exposure of the plastic to the ultra-violet radiation from the sun, such that the bag would ultimately crack thereby exposing the interior of the vent to the elements, unbeknownst to individuals on the ground. The second problem with the clear plastic bags is that it is possible for them to become easily dislodged from the top of the vent stacks, absent any blow off from the tank itself. This dislodgement often occurs in time of bad weather.
Thus, previously utilized methods of covering vent stacks have not been found adequate to prevent the introduction of foreign matter into the vent stacks, nor are they readily capable of being maintained in a secured relationship atop the vent stacks under severe weather conditions. Therefore, it is apparent that the need exists for an improvement in blow off caps. Additionally, from a practical standpoint, the improvement cannot be extremely costly nor can it unduly disrupt present vent stack configuration.